A plasma is a collection of charged particles, containing about equal numbers of positive ions and negative ions plus electrons. It is typically an aeroform fluid, like a gas but, unlike most gases, a plasma is a relatively good conductor of electricity and is affected by magnetic fields.
Plasmas can be formed in different ways. One method of forming a plasma is by creating an electrical potential differential between two electrodes that have a medium between them, such as a gas. As the potential increases between the plates, the positive portions of the gas are drawn toward the negatively charged electrode, and the negative portions of the gas are drawn toward the positively charged electrode. At a certain potential, the valence electrons or other negative components of certain gases are torn from the rest of the species, creating positive ions, negative ions, and free electrons. These ions and electrons tend to dissociate as described above and recombine repeatedly in the plasma. However, during the times when they exist as charged species, they tend to make the plasma very reactive.
Plasma generation devices are powered by radio frequency current sources, lower frequency alternating current sources, or direct current sources. Electrodes are fashioned from both metallic and nonmetallic materials. However, direct current sources do not tend to work reliably with metallic or nonmetallic electrodes but, rather, tend to initially arc from a somewhat random location, and then preferentially arc from that location thereafter. Thus, the combination of direct current and nonmetallic electrodes typically does not produce a uniform and well defined plasma.
A radio frequency current source can be used with nonmetallic electrodes to form a uniform plasma. However, radio frequency current sources tend to be somewhat inefficient and have other drawbacks in certain applications. For example, radio frequency current sources have a detectable radio frequency signature, which may be undesirable. They also tend to be more expensive than direct current sources. Thus, there is a need for a direct current plasma generation system that will not arc.